This invention relates to captive screws of the type generally used to attach a first panel to a second panel, frame or other surface wherein it is desired to keep the fastener in position on the first panel without loose items of hardware. The captive screw is mounted to the upper panel such that the screw stays attached to the panel even when the threads of the screw are fully disengaged from a threaded hole in the second panel to which the first panel is attached.
The present invention is directed toward a new and improved captive screw of a type which has a knob, a screw, and a ferrule. The captive screw is captivated on a panel by the ferrule and as the screw is screwed into a second panel the knob telescopically retracts over the ferrule. A spring may be used which urges the knob and integral screw to its fully retracted position when the captive screw is not attached to the second panel, thereby withdrawing the threads of the screw from the area of the lower panel.
Captive screws of the foregoing type in general are disclosed in, for example, Frattarola, U.S. Pat. No. 5,382,124 and French Patent 1,339,942. These patents depict captive screws of the general type herein but contain different configurations where the screw head mates integrally with the knob of the captive screw.
This invention relates to a low profile, retractable captive screw of the type wherein a first panel or other thin flat surface is to be mounted against another surface, such as a second panel or frame. The captive screw of the present invention has a unique configuration in the means by which the screw portion of the captive screw is mounted to the knob of the captive screw. The screw is attachable to the first panel, and is used for attaching the first panel to a lower surface, the lower surface having a threaded hole. The captive screw has a screw with or without an added flange surrounding the periphery of the head of the screw with protrusions integral to the outer perimeter of the screw head or flange, a thin-walled, cylindrical hollow knob that rigidly attaches to the screw, a ferrule that attaches to the upper panel and to the knob, and a spring. The flange with the protrusions or the screw head with the protrusions rigidly secures the screw head to the inner surface of the knob and provides a press-fit of the screw to the inner surface of the knob. The flange, if used, provides significant advantages in that it provides for a positive stop when the screw is pressed into the knob. Further, the screw head is installed into the knob from the bottom side of the knob rather than the top side of the knob as in similar prior art screws, providing further advantages as described below.
A second means for attachment of the screw to the knob allows for a press fit of the screw into the knob by filling in a chamfer on the periphery of the screw with material from the inner surface of the knob. This new construction provides significant structural advantages over prior art captive screws. The screw applies force directly through the ferrule rather than through a portion of the knob as in some similar prior art screws. The construction of the knob/screw interface allows for insertion of the screw into the bottom of the knob, rather than the top of the knob. In failure of the knob screw interface, the captive screw of the present invention still retains the panels to which the captive screw is attached. Even if the knob breaks free of the screw while the screw is in the open position, the knob is still retained on the screw, the screw is retained in the captive screw assembly, and the screw functions.
It is therefore an object of the present invention to provide a captive screw that provides for an improved, stronger knob/screw interface.
It is a further object of the present invention to provide a captive screw that provides for an improved, stronger knob/screw interface that provides for more surface area and therefore a stronger assembly, particularly when the captive screw is pressed onto a panel.
Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.